Capacitors are electrical components that have the capability of storing electrical energy. This energy is stored in an electrostatic field that is created by electrical charges accumulating on conducting plates placed across an electrical potential and separated by an insulating medium such as ceramics, for example barium titanate (BaTiO3), magnesium titanate (MgTiO3). These ceramic capacitors are used in various applications such as in temperature compensation, in semiconductors, and in applications requiring various dielectric constants, for example Low K class I ceramics and Higher K class II ceramics.
A conventional structure for ceramic capacitors is a structure of multiple layers in which dielectric layers of ceramic are interleaved with conductive electrodes. Alternating conductive electrodes are electrically connected, resulting in a device having two effective electrodes with a capacitance many times the capacitance of the single dielectric layer, packed in a relatively very small volume. These multilayer ceramic capacitors (MLCCs) are the most reliable component for high energy density storage banks. This type of capacitor has been developed to meet demands for high-density ceramic capacitors.
MLCCs consist of a plurality of interleaved and staggered layers of an electrically conductive film of metal known as electrodes, formed by the deposition (usually by screen printing or the like) of a thick film paste or ink, and electrically insulating layers of a dielectric ceramic oxide, formed by laying a cast dielectric tape or by casting a dielectric slurry over the dried electrode. Such capacitors are well known in the art. U.S. Pat. No. 2,389,420, for example, describes the structure, manufacture and properties of monolithic multilayer ceramic capacitors formed using cast dielectric green (unfired) tape.
In a typical MLCC the end termination provides the vital electrical path between the inner electrodes and components exterior to the capacitor. A typical end termination is made by post firing an end termination ink on a pre fired MLCC structure. A typical end termination ink comprises metal particles and glass particles dispersed in an organic medium. Despite its relatively small proportion in an end termination ink, glass plays a major role in providing adhesion to the capacitor body, providing thermal expansion matching between metal and the capacitor body to avoid cracking at the interface, ensuring good metal densification, allowing a wider firing window, and preventing penetration of plating solution into the termination during subsequent processing.
Multi-layered ceramic capacitors incorporate multiple printed layers of electrode plates made of thin ceramic sheets, (e.g., thickness 10 to 20 μm). These capacitors are more compact and have better temperature characteristics than single-layered ceramic capacitors. Air fired conventional multi-layered ceramic capacitors are, however, rather expensive because their electrode plates use precious metals, such as silver, gold, platinum, palladium and alloys thereof. Therefore MLCCs with base metal electrodes have been developed. However these have to be fired in atmospheres containing very little O2, such as N2 atmosphere with less than 10 ppm oxygen. Development of novel reduction resistant end termination inks in general, and reduction resistant Pb free and Cd free glasses for use in termination ink in particular, is the subject of this present invention.